1. Field of the Invention
The present invention relates to a pneumatic radial tire for heavy duty use improved in the bead durability.
2. Description of Related Art
In heavy duty tires for trucks, buses and the like, the tire pressure is relatively high and the carcass cord tension which pull the carcass turnup portion (f) radially inwardly as shown in FIG. 4 is also high. Further, the tire load is relatively high. The sidewall portion (d) and bead portion (e) are repeatedly subjected to large bending deformation during running, and the stress concentrates on the end (h) of the turnup portion (f) of the carcass (g), and the end (h) is liable to separate from the surrounding rubber to greatly decrease the durability.
Thus, to prevent such a separation failure, conventionally, a bead reinforcing layer (k) shown in FIG. 4 is disposed in the bead portion (e) to secure the carcass ply between the bead core (j) and this layer (k). This bead reinforcing layer (k) however, involves another problem, that is, separation failure at the axially inner end (m) and axially outer end (n) of the bead reinforcing layer (k) due to sharing stress between the carcass (g) and this layer. Further, as the rigidity of the bead portion is increased, this bead reinforcing layer has a tendency to make the rim mounting operation difficult and deteriorate the ride comfort. This is especially remarkable when steel cords are used in the reinforcing layer.